The field of the invention is laser-based alignment equipment, and particularly, systems which produce an alignment field using a laser and one or more receivers which detect the field and provide an accurate alignment indication at locations remote from the laser transmitter.
In prior laser-based alignment systems such as that disclosed in U.S. Pat. No. 3,588,249, a columnated laser beam is rotated 360.degree. about an axis to establish an alignment plane. Remote receivers in the vicinity may detect the laser beam as it sweeps past, and provide a visual or audible indication when they are aligned in the laser plane. While this rotating beacon technique provides excellent results over long ranges, the cost of the mechanical and optical structures for implementing the technique with the desired amount of accuracy is relatively high. In addition, the plane is more difficult to locate, as the receiver may be moved through the plane before the beam strikes its detector.
Another technique for producing an alignment plane or cone with a laser is to direct a columnated laser beam at a conical surface. The laser beam is separated by the surface and each portion is reflected directly from the cone at angle to produce a continous laser alignment plane or cone which extends radially outward from the conical surface over 360.degree.. While this technique eliminates the need for a rotating mechanism, the laser energy directed in any single direction is only a small fraction of the total beam energy. As a result, the range of the instrument is substantially reduced when used with receivers having the same sensitivity. Of course, the laser beam energy could be increased to offset this loss, but the increased cost, size and energy consumption of the larger laser offsets much of the cost advantage of this technique. Also, government regulations severely limit the energy level of lasers which can be used in the workplace.
When the laser transmitter is employed on a construction site, it is typically mounted on a tripod or other structure which can be precisely adjusted to level the laser plane which it produces. The receivers may be carried by construction workers or mounted on earth moving equipment and used throughout a large area. Such workers or equipment operators must be warned immediately if the laser alignment plane is out of level. This may occur, for example, on windy days, or when large equipment is operated near the laser transmitter.